不知为何，忽然发现自己使用catkin_make编译空的功能包竟然也能报错，
自己的操作为

mkdir -p wu_ws/src
cd work_ws
catkin_make

正常来讲，空的包是能直接编译通过的。但是竟然发生了如下错误。
具体报错如下：

CMake Error: File /home/wuxr/graspping/realsense_ws/src/package.xml does not exist.
CMake Error at /opt/ros/melodic/share/catkin/cmake/stamp.cmake:10 (configure_file):
  configure_file Problem configuring file
Call Stack (most recent call first):
  /opt/ros/melodic/share/catkin/cmake/catkin_package_xml.cmake:72 (stamp)
  /opt/ros/melodic/share/catkin/cmake/catkin_package_xml.cmake:50 (_catkin_package_xml)
  /opt/ros/melodic/share/catkin/cmake/catkin_package.cmake:99 (catkin_package_xml)
  CMakeLists.txt:46 (catkin_package)


CMake Error at /opt/ros/melodic/share/catkin/cmake/catkin_package.cmake:116 (message):
  catkin_package() 'catkin' must be listed as a buildtool dependency in the
  package.xml
Call Stack (most recent call first):
  /opt/ros/melodic/share/catkin/cmake/catkin_package.cmake:102 (_catkin_package)
  CMakeLists.txt:46 (catkin_package)


-- Configuring incomplete, errors occurred!
See also "/home/wuxr/graspping/realsense_ws/build/CMakeFiles/CMakeOutput.log".
See also "/home/wuxr/graspping/realsense_ws/build/CMakeFiles/CMakeError.log".
Invoking "cmake" failed

打开在src下面的CMakeLists.txt，因此仔细一看，好像和平常的CMakelists.txt文件不太一样，像是个软链接。于是运行ls -l后，发现真是，它指向了一个cmake。而且打开后，发现他是我之前做的一个ros包用到的CMakelist文件。所以报错了。。。。

(base) wuxr@wuxr:~/wu_ws/src$ ls -l
总用量 0
lrwxrwxrwx 1 wuxr wuxr 50 4月  16 20:25 CMakeLists.txt -> /opt/ros/melodic/share/catkin/cmake/toplevel.cmake

百度一番，有个哥们的解答有用。
将src下面的CMaklists.txt软链接删除，重新创建文件CMakeLists，复制以下代码到该文件。

# toplevel CMakeLists.txt for a catkin workspace
# catkin/cmake/toplevel.cmake

cmake_minimum_required(VERSION 2.8.3)

set(CATKIN_TOPLEVEL TRUE)

# search for catkin within the workspace
set(_cmd "catkin_find_pkg" "catkin" "${CMAKE_SOURCE_DIR}")
execute_process(COMMAND ${_cmd}
  RESULT_VARIABLE _res
  OUTPUT_VARIABLE _out
  ERROR_VARIABLE _err
  OUTPUT_STRIP_TRAILING_WHITESPACE
  ERROR_STRIP_TRAILING_WHITESPACE
)
if(NOT _res EQUAL 0 AND NOT _res EQUAL 2)
  # searching fot catkin resulted in an error
  string(REPLACE ";" " " _cmd_str "${_cmd}")
  message(FATAL_ERROR "Search for 'catkin' in workspace failed (${_cmd_str}): ${_err}")
endif()

# include catkin from workspace or via find_package()
if(_res EQUAL 0)
  set(catkin_EXTRAS_DIR "${CMAKE_SOURCE_DIR}/${_out}/cmake")
  # include all.cmake without add_subdirectory to let it operate in same scope
  include(${catkin_EXTRAS_DIR}/all.cmake NO_POLICY_SCOPE)
  add_subdirectory("${_out}")

else()
  # use either CMAKE_PREFIX_PATH explicitly passed to CMake as a command line argument
  # or CMAKE_PREFIX_PATH from the environment
  if(NOT DEFINED CMAKE_PREFIX_PATH)
    if(NOT "$ENV{CMAKE_PREFIX_PATH}" STREQUAL "")
      string(REPLACE ":" ";" CMAKE_PREFIX_PATH $ENV{CMAKE_PREFIX_PATH})
    endif()
  endif()

  # list of catkin workspaces
  set(catkin_search_path "")
  foreach(path ${CMAKE_PREFIX_PATH})
    if(EXISTS "${path}/.catkin")
      list(FIND catkin_search_path ${path} _index)
      if(_index EQUAL -1)
        list(APPEND catkin_search_path ${path})
      endif()
    endif()
  endforeach()

  # search for catkin in all workspaces
  set(CATKIN_TOPLEVEL_FIND_PACKAGE TRUE)
  find_package(catkin QUIET
    NO_POLICY_SCOPE
    PATHS ${catkin_search_path}
    NO_DEFAULT_PATH NO_CMAKE_FIND_ROOT_PATH)
  unset(CATKIN_TOPLEVEL_FIND_PACKAGE)

  if(NOT catkin_FOUND)
    message(FATAL_ERROR "find_package(catkin) failed. catkin was neither found in the workspace nor in the CMAKE_PREFIX_PATH. One reason may be that no ROS setup.sh was sourced before.")
  endif()
endif()

catkin_workspace()

保存后，在cd wu_ws回到工作空间,执行caktin_make。成功编译。